Generally, a battery pack of a large electric vehicle comprises several hundreds of batteries. These batteries are connected with each other in parallel or in series. However, if the battery contacts are not securely locked, the batteries of the battery pack are possibly loosened. Especially, when the electric vehicle is driven on a road with a poor condition, the vibration of electric vehicle may accelerate the problem of loosening the battery contacts. If the battery contacts are loosened or poorly contacted during the travelling process of the electric vehicle, the overall power system is possibly shut down or burnt out.
However, the conventional electrode connecting method cannot indicate whether the electrodes are certainly locked. If the battery pack is suffered from a poor contact problem, the worker cannot immediately realize the damaged site. Under this circumstance, the time period of checking the battery pack is largely increased. Moreover, since the electric vehicle is only powered by the battery pack, the reliability of the battery pack is an important factor influencing performance of the electric vehicle.